The present invention relates to a light position sensor which has a photosensitive semiconductor element including a photosensitive surface composed of a reverse-biased pn junction formed between a pair of electrodes, and a processing circuit.
When a narrow beam of light is projected onto the photosensitive surface between the electrodes, the semiconductor element provides photocurrents which are taken, respectively, from the electrodes, and which vary in dependence on the position of illumination between the electrodes in such a manner that the total photocurrent is divided into the two photocurrents of the electrodes at a ratio determined by the position of illumination. The processing circuit processes the photocurrents from the electrodes to determine the position of illumination.